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<a name="boost.proto._data"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle">Struct _data</span></h2>
<p>boost::proto::_data &#8212; 
          A <a class="link" href="../../PrimitiveTransform.html" title="Concept PrimitiveTransform">PrimitiveTransform</a> that returns the current data unmodified.
          If the data (third) parameter is a transform environment, it returns the value associated
          with the <code class="computeroutput"><a class="link" href="data_type.html" title="Struct data_type">proto::data_type</a></code> key. Otherwise, it returns
          the data parameter unmodified.
        </p>
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<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../proto/reference.html#header.boost.proto.transform.arg_hpp" title="Header &lt;boost/proto/transform/arg.hpp&gt;">boost/proto/transform/arg.hpp</a>&gt;

</span>
<span class="keyword">struct</span> <a class="link" href="_data.html" title="Struct _data">_data</a> <span class="special">:</span> <span class="keyword"></span> <a class="link" href="transform.html" title="Struct template transform">proto::transform</a><span class="special">&lt;</span> <span class="identifier">_data</span> <span class="special">&gt;</span> <span class="special">{</span>
  <span class="comment">// member classes/structs/unions</span>
  <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <a class="link" href="../../Expr.html" title="Concept Expr">Expr</a><span class="special">,</span> <span class="keyword">typename</span> State<span class="special">,</span> <span class="keyword">typename</span> Data<span class="special">&gt;</span> 
  <span class="keyword">struct</span> <a class="link" href="_data/impl.html" title="Struct template impl">impl</a> <span class="special">:</span> <span class="keyword"></span> 
    <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">if_c</span><span class="special">&lt;</span>
      <a class="link" href="is_env.html" title="Struct template is_env">proto::is_env</a><span class="special">&lt;</span><span class="identifier">Data</span><span class="special">&gt;</span><span class="special">::</span><span class="identifier">value</span><span class="special">,</span>
      <a class="link" href="_env_var.html" title="Struct template _env_var">proto::_env_var</a><span class="special">&lt;</span><a class="link" href="data_type.html" title="Struct data_type">proto::data_type</a><span class="special">&gt;</span><span class="special">,</span>
      <a class="link" href="_env.html" title="Struct _env">proto::_env</a>
    <span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span><span class="special">::</span><span class="keyword">template</span> <span class="identifier">impl</span><span class="special">&lt;</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">State</span><span class="special">,</span> <span class="identifier">Data</span><span class="special">&gt;</span>
  <span class="special">{</span>
  <span class="special">}</span><span class="special">;</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idp141840672"></a><h2>Description</h2>
<p>
            If the data (third) parameter is a transform environment, it returns the value associated
            with the <code class="computeroutput"><a class="link" href="data_type.html" title="Struct data_type">proto::data_type</a></code> key. Otherwise, it returns
            the data parameter unmodified.
          </p>
<p>
            <span class="bold"><strong>Example:</strong></span>
            </p>
<pre class="programlisting"><a class="link" href="terminal.html" title="Struct template terminal">proto::terminal</a><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span> <span class="identifier">i</span> <span class="special">=</span> <span class="special">{</span><span class="number">42</span><span class="special">}</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">str</span><span class="special">(</span><span class="string">"hello"</span><span class="special">)</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&amp;</span> <span class="identifier">d1</span> <span class="special">=</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">_data</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="char">'a'</span><span class="special">,</span> <span class="identifier">str</span><span class="special">)</span><span class="special">;</span>
<span class="identifier">assert</span><span class="special">(</span> <span class="special">&amp;</span><span class="identifier">str</span> <span class="special">==</span> <span class="special">&amp;</span><span class="identifier">d1</span> <span class="special">)</span><span class="special">;</span>

<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&amp;</span> <span class="identifier">d2</span> <span class="special">=</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">_data</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="char">'a'</span><span class="special">,</span> <span class="special">(</span><a class="link" href="data.html" title="Global data">proto::data</a> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ref</span><span class="special">(</span><span class="identifier">str</span><span class="special">)</span><span class="special">)</span><span class="special">)</span><span class="special">;</span>
<span class="identifier">assert</span><span class="special">(</span> <span class="special">&amp;</span><span class="identifier">str</span> <span class="special">==</span> <span class="special">&amp;</span><span class="identifier">d2</span> <span class="special">)</span><span class="special">;</span></pre>
<p>
          </p>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2008 Eric Niebler<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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